No one (what ever their size) needs the pressure to feel positive about their body all the time. It isn't realistic. You're going to have a bad thought (or two) about how you look from time to time but don't feel bad about it.
Instead, I encourage you to change your mindset and be 'body neutral'. Accept that it's ok not to be ok with your body twenty-four-seven. Live your life what ever your size. Embrace self love instead and be in charge of your own happiness.